1. Field of the Invention
The present invention relates to a catalyst-aided chemical processing method and apparatus, and more particularly to a catalyst-aided chemical processing method and apparatus for processing a workpiece by utilizing a catalytic action capable of chemical reaction.
2. Description of the Related Art
Mechanical processing methods have long been used in various fields. A mechanical polishing method, for example, involves pressing a tool against a surface to be processed so as to process the surface by creating material defects in the surface and taking away surface atoms through a mechanical action. Such a mechanical polishing method causes damage to a crystal lattice and, in addition, can hardly provide a high-accuracy processed surface. In order to process a workpiece with high accuracy, it is necessary to use a chemical processing method which can process the workpiece without producing a lattice defect in it.
A processing method called EEM (elastic emission machining) is known which involves allowing a suspension of ultrafine powder to flow along a surface to be processed of a workpiece so as to bring the ultrafine powder into contact with the surface to be processed, without applying a substantial load on it, and processing the surface to be processed by removing surface atoms of the surface to be processed on the order of atomic unit through an interaction (sort of chemical bonding) between the ultrafine powder and the surface to be processed (see, for example, Japanese Patent Laid-Open Publication No. 2000-167770, and Japanese Patent Publications Nos. H2-25745, H7-16870 and H6-44989).
Further, plasma CVM (chemical vaporization machining) has been proposed which is a processing method comprising supplying a neutral radical, which has been produced by decomposition of a reactive gas caused by high-voltage application to a processing electrode, to a surface to be processed of a workpiece while moving the processing electrode relative to the surface to be processed, thereby processing the surface to be processed through vaporization and removal of a volatile compound produced by a radical reaction between the neutral radical and an atom or a molecule of the surface to be processed (see, for example, Japanese Patent No. 2962583). Upon the processing, the processing time is numerically controlled based on processing time-processing amount correlation data, determined by the type of the reactive gas and the material of the workpiece, and also on coordinate data regarding a pre-processed surface and an intended post-processed surface, and according to the coordinate difference.
A high-efficiency processing method utilizing a high-density radical reaction has also been proposed which involves rotating a rotary electrode at a high speed to bring in a gas with the surface of the rotating electrode, thereby creating a flow of the gas that passes through a processing gap (see, for example, Japanese Patent No. 3069271).
The above-described EEM and plasma CVM are both excellent chemical processing methods. The EEM method can provide a flat processed surface at an atomic level. High-efficiency processing, comparable to mechanical processing, can be performed with high accuracy by plasma CVM.
As will be appreciated from the processing principle of EEM, it is possible with EEM to obtain a very flat processed surface for a high-frequency space wavelength. In EEM, fine particles of, e.g., SiO2 are supplied by ultrapure water to a surface to be processed of a workpiece, and processing progresses through chemical bonding between surface atoms of the fine particles and surface atoms of the workpiece. It would appear that the surfaces of the fine particles constitute a very flat plane and the flat plane will be transferred as a reference plane to the surface to be processed. It is therefore possible to obtain a flat processed surface at an atomic level without disordering atomic arrangement. Because of the processing principle, however, it is difficult with EEM to flatten a surface of a space wavelength range of not less than several tens of μm.
Because of the use of an active radical, plasma CVM is a high-efficiency processing method. Plasma CVM utilizes a chemical reaction between neutral radicals in a plasma and the surface of a workpiece. In particular, processing is carried out by generating a high-density plasma in a high-pressure atmosphere of 1 atm and causing neutral radicals generated in the plasma to act on surface atom of a workpiece to convert the atoms into a volatile substance. Plasma CVM can thus process a surface to be processed with a high processing efficiency, comparable to conventional mechanical processing, without entailing disorder of atomic arrangement in the surface to be processed. With no reference plane, however, the processing is likely to be affected by the plane index, lattice defects, etc. of the processing surface.
Chemical mechanical polishing (CMP), on the other hand, uses abrasive grains of, for example, SiO2 or Cr2O3, and is directed to forming a non-disturbed processed surface by utilizing a chemical action and thus with a less mechanical action. For example, Japanese Patent No. 3734722 discloses a method which comprises immersing a diamond film in an oxidizing polishing liquid in which abrasive grains, having catalytic oxidizing properties, are dispersed, and polishing the diamond film while rubbing the surface of the film with the abrasive grains. The patent document discloses the use of chromium oxide or iron oxide as the abrasive grains and the use of a polishing liquid comprising a dispersion of the abrasive grains in a hydrogen peroxide solution, or an aqueous nitrate solution or a mixture thereof. Because of the mechanical factor of CMP, however, it is not possible with CMP to completely remove a denatured processed layer. In addition, CMP can hardly be employed for processing of a material having a low mechanical rigidity.
A processing method has been proposed which comprises putting a workpiece in a processing liquid, in particular a hydrohalic acid, bringing a solid catalyst composed of platinum, gold or a ceramic material into contact with or close proximity to a surface to be processed of the workpiece, and dissolving in the processing liquid a halogen compound formed by a chemical reaction between a halogen radical and a surface atom of the workpiece, the halogen radical being generated by the dissociation of a hydrogen halide molecule at the surface of the catalyst, thereby processing the workpiece (see, for example, Japanese Patent Laid-Open Publication No. 2006-114632). However, there exist materials that cannot be processed with a halogen radical. GaN, for example, is stable in hydrofluoric acid and thus cannot be processed with a halogen radical (fluorine radical). Hydrofluoric acid cannot be used for processing of copper because copper corrodes rapidly in hydrofluoric acid.
It is known that surface atoms of a workpiece can be ionized and etched away by immersing the workpiece in a processing liquid comprising a mixture of an oxidizing solution and an acidic or basic solution suited for the metal material of the workpiece. According to this processing method, a surface to be processed of a workpiece is etched away uniformly, that is, a surface roughness of the processed surface cannot be improved. Thus, it is generally difficult with this method to process a surface into a flat processed surface. This method also involves the problem that an etching reaction progresses even after processing due to a processing liquid remaining on the workpiece. Replacement of the remaining processing liquid, e.g., with ultrapure water immediately after processing is therefore needed.